JPS6054156B2 - Flux for submerged arc welding of ultra-low carbon austenitic stainless steel - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a flux for latent arc welding of austenitic stainless steel, and more specifically, a flux used for latent arc welding of ultra-low carbon austenitic stainless steel with a carbon content of 0.02% or less. This flux is used to improve corrosion resistance by suppressing the carbon content of weld metal to the same level or lower than that of the base metal.

As is well known, stainless steel is widely used in industry because it is a material with many excellent properties such as corrosion resistance, high temperature strength, and low temperature toughness.

However, in recent years, the environment in which they are used has become even more harsh.
In addition, since the required standards are becoming more stringent, various studies have been made to further improve the conventional performance so as to be able to meet diversifying requirements.

That is, it is well known that low carbonization and the addition of carbon stabilizing elements (typically Ti and Nb) are effective in improving the corrosion resistance of stainless steel, such as intergranular corrosion and stress corrosion resistance. This is where I am.

As mentioned above, to obtain even higher performance, Ta, Mo
Although there are composite additions of carbon stabilizing elements such as , W, and V, when weldability and other mechanical properties are taken into account, the most straightforward approach is to minimize the carbon content, and recent steelmaking technology requires 0.
01%C or less has reached the stage where it can be put to practical use. On the other hand, when welding these stainless steels, welding methods that use flux, such as covered arc welding and submerged arc welding, have problems with welding workability, such as arc stability, slag peeling, heat appearance, and other issues related to these. Due to restrictions on welding defects such as slag inclusions and blowholes, it has been difficult to create a flux composition that reduces carbon penetration into the weld metal.

In other words, ordinary bond flux for submerged arc welding contains about 5 to 20% carbonate, mainly lime carbonate (CaCO3), and its function is to decompose with welding heat and generate CO2 gas, The purpose is to stabilize the arc by stabilizing the gas composition of the atmosphere and lowering the partial pressure of nitrogen, hydrogen, etc. to obtain a sound weld.

However, the generated CO2 gas dissociates in the arc atmosphere and increases carbon in the weld metal.

In this case, the base material to be welded is carbon steel, low alloy steel or 0.
In the case of ordinary austenitic stainless steel containing about 0.03 to 0.08% carbon, the amount of increase in carbon due to CO2 gas generated from flux is minute compared to the carbon content of the base material, so it is not so much. Although this is not a problem, when welding ultra-low carbon austenitic stainless steel, it is extremely undesirable to add carbonates that have such an effect to the flux, as this will cause various adverse effects due to the increase in carbon in the weld metal. . Therefore, a few methods have already been proposed to reduce the carbon content of weld metal, but none of them have yet been designed to achieve sound welding without adding carbonate to the flux. There is.

For example, the flux described in Japanese Patent Publication No. 51-31782 contains 10 to 45% of metal fluoride, which is vaporized by welding heat.
It is a combination.

However, it is impossible to achieve stable welding simply by adding a large amount of metal fluoride, and even if this flux is applied to submerged arc welding of ultra-low carbon austenitic stainless steel, slag seizure or bead appearance will be significant. It is hard to say that it is inferior or practical. In addition, the special public
In No. 2-19814, a slag agent, a deoxidizing agent, an alloying agent, etc. were mixed into a glassy powder obtained by melting and pulverizing the powder in advance, and the mixture was granulated and sintered. There is an example of flux for submerged arc welding of austenitic stainless steel, but in this case as well, it must be melted and then crushed again, blended as part of the raw material, granulated, and sintered before use. It was a flux with very low productivity. The present invention relates to a flux for submerged arc welding of ultra-low carbon austenitic stainless steel that completely eliminates these drawbacks. It is used in combination with steel wire, and its composition is CaF2, AlF3, MgF'2, BaF2, Na
The total amount of fluorides consisting of one or more of F, LiF or Na3AlF6 is 45-80%, Al2O3l
O~40%, ZrO23~25% are essential components, Ca
Limit cO3 to 7% or less, and the remainder is SiO2, MnO, TiO2, MgOl, which are usually used for bond flux.
For submerged arc welding of ultra-low carbon austenitic stainless steel, characterized by comprising a total of 4 to 16% of one or more of Ni, Cr, MO, Nb metal powder or alloy powder or iron alloy powder, and unavoidable impurities. It's in Flux.

The present invention will be explained in detail below.

First, the flux of the present invention is used in combination with ultra-low carbon austenitic stainless steel wire having a carbon content of 0.02% or less.

As mentioned above, when welding ultra-low carbon austenitic stainless steel, the carbon content of the wire used is of course important in order to keep the carbon content of the resulting weld metal as low as possible. In order to make the amount of carbon less than 0.02%, the amount of carbon in the wire used must be less than 0.02%. If the carbon content of the wire exceeds 0.02%, even if welded in combination with the high-performance flux according to the present invention, the carbon content in the weld metal will be reduced to 0.02%.
It cannot be suppressed below %.

Next, we will discuss the reasons for limiting the flux components. First, the major features of the flux of the present invention are CaF2, AlF3
, MgF2, BaF2, NaF, LlF or Na3
This is because the total amount of fluorides consisting of one or more types of AlF6 is extremely large.

All of these fluorides exist in the arc atmosphere and have the effect of increasing the potential gradient.

This means that the arc length is shorter for the set voltage than when using normal flux, and this was confirmed by directly observing the submerged arc welding phenomenon using X-ray transmission method. Ta. This reduces the amount of molten metal exposed directly into the arc cavity, thus having a significant effect in reducing carbon migration from the CO2 gas to the weld metal. In this case, the total content of one or more fluorides was limited to 45 to 80%, which is 45%.
If it is less than 1, the above-mentioned effects will not be sufficient, and it will not be possible to sufficiently prevent carbon from entering the weld metal.

On the other hand, if it exceeds 80%, the arc becomes extremely unstable during welding, making it impossible to obtain a sound weld bead. Furthermore, all of these fluorides have melting points of about 1000 to 1350.
Since slag is formed with a low viscosity of 0.degree. C., the slag covers the molten metal during welding and protects it from the atmosphere.

Therefore, a sound weld metal can be obtained even if the amount of carbonate such as CacO3 is significantly lower than that of a normal bond flux.

Next, 10 to 40% of Al2O3 is suitable.

In bond flux containing a large amount of fluoride, Al2
The main effect of O3 is to adjust welding workability. Al
If the amount of 2O3 is less than 10%, practical welding cannot be performed because it is impossible to prevent the melting point and viscosity of the slag from lowering due to the large amount of fluoride blended. On the other hand 4
If the content exceeds 0%, the melting point of the slag will become too high and welding workability will deteriorate significantly. In addition, ZrO2 is 3~
25% is required.

The problem with using a flux containing a large amount of fluoride is arc stability and bead appearance. By adding ZrO2, these two problems are solved at once, and beautiful beads can be easily obtained.

Here, if the amount of ZrO2 is less than 3%, the effect will not be sufficient, and if it is added in excess of 25%, the composition system of the slag will be shifted, and welding workability will be adversely affected.

Therefore, in the present invention, the amount of ZrO2 added is limited to 3 to 25%. As mentioned above, the flux of the present invention has a characteristic effect due to the combination of a large amount of fluoride, for example, CacO3.
Even if the weld metal contains up to 7% carbonate, the carbon content in the weld metal can be as low as the aim of the present invention.

Therefore, if the amount is 7% or less, carbonate can be added to further expand the application range of the flux. Regarding other components, the metals such as SlO2, MrO, TiO2, MgOl, which are usually used in bond flux, and the metals Ni, Cr, MO, and Nb, which are usually added to bond flux for submerged arc welding of austenitic stainless steel. A total of 4 to 1 types of powder, alloy powder, or iron alloy powder
6%, there is no problem even if it is used.

Although the flux of the present invention is used to fully demonstrate its performance when used for welding ultra-low carbon austenitic stainless steel with a carbon content of 0.02% or less, it does not cause any problems when used with ordinary austenitic stainless steel. Needless to say, there is no such thing. Next, examples of the present invention will be shown. 1st
Table 2 shows the composition of the flux, Table 2 shows the chemical composition of the wire, and Table 3 shows the chemical composition of the base material.

The groove was a 60 V groove with a root face of 3TIr1n, and was finished by two-bus welding on both sides. The welding conditions were 400A-32V-45 (1/Min) for each bus, and an AC power source was used.The test results are shown in Table 4.In the examples of the present invention, welding workability is sufficient for practical use in all cases. It has no defects or is grade 1 class 2 in the X-ray transmission test,
The C% of the weld metal was also low at 0.016 to 0.018%.

Claims (1)

[Claims] 1 Used in combination with ultra-low carbon austenitic stainless steel wire with a carbon content of 0.02% or less, the composition of which is CaF_2, AlF_2, MgF_2, BaF
_2, NaF, LiF or Na_3AlF_6 1
The total amount of fluoride consisting of species or two or more species is 45-80%
, Al_2O_310-40%, ZrO_23-25%
is an essential component, CaCO_3 is limited to 7% or less, and the remainder is SiO_2, M, which is usually used for bond flux.
nO, TiO_2, MgO, and Ni, Cr, Mo, N
A flux for submerged arc welding of ultra-low carbon austenitic stainless steel, characterized by comprising a total of 4 to 16% of one or more of (b) metal powder, alloy powder, or iron alloy powder, and unavoidable impurities.